The improbable primate : how water shaped human evolution PDF
Preview The improbable primate : how water shaped human evolution
THE IMPROBABLE PRIMATE 3 GreatClarendonStreet,Oxford,OXDP, UnitedKingdom OxfordUniversityPressisadepartmentoftheUniversityofOxford. ItfurtherstheUniversity’sobjectiveofexcellenceinresearch,scholarship, andeducationbypublishingworldwide.Oxfordisaregisteredtrademarkof OxfordUniversityPressintheUKandincertainothercountries #CliveFinlayson Themoralrightsoftheauthorhavebeenasserted FirstEditionpublished Impression: Allrightsreserved.Nopartofthispublicationmaybereproduced,storedin aretrievalsystem,ortransmitted,inanyformorbyanymeans,withoutthe priorpermissioninwritingofOxfordUniversityPress,orasexpresslypermitted bylaw,bylicenceorundertermsagreedwiththeappropriatereprographics rightsorganization.Enquiriesconcerningreproductionoutsidethescopeofthe aboveshouldbesenttotheRightsDepartment,OxfordUniversityPress,atthe addressabove Youmustnotcirculatethisworkinanyotherform andyoumustimposethissameconditiononanyacquirer PublishedintheUnitedStatesofAmericabyOxfordUniversityPress MadisonAvenue,NewYork,NY,UnitedStatesofAmerica BritishLibraryCataloguinginPublicationData Dataavailable LibraryofCongressControlNumber: ISBN –––– PrintedinItalyby L.E.G.O.S.p.A. CONTENTS ListofIllustrations vi Preface vii . TheInvertedPanda . AndtheWorldChangedForever . AttheLake’sEdge . TheFirstHumans . MiddleEarth:TheHomeoftheFirstHumans . TheDryingWorldoftheMiddlePleistocene . TheRainChasers—SolutionsinaDryingWorld . TheExceptionalWorldoftheNeanderthal . GlobalExpansionoftheRainChasers . Australia . FromLakeChadtoPuritjarraandBeyond Endnotes Index v LIST OF ILLUSTRATIONS . MapshowingthegeographicalextentofMiddleEarth xiii . Griffonvulturesfeastingonacarcass . Thehumanhabitat:trees/open-spaces/water . Howtechnologiescancoexist,survive,anddisappear . SequenceshowinghowtheHimalayanlaunchpadworks – . TheWaterOptimizationModel vi PREFACE NEVER MORE THAN ONE SPECIES OF MAN... In,ErnstMayrwroteaboutourspeciesandourevolutionin a Cold Spring Harbor symposium which was dedicated to the origin and evolution of man.1 The symposia held at the Cold Spring Harbor Laboratory in New York since have debated majordiscoveriesinbiologyandarehighlyregardedaslandmark meetings. Mayr was one of the century’s leading and highly respected evolutionary biologists and a key contributor to the modern evolutionary synthesis. In he had published a sem- inal book Systematics and the Origin of Species from the Viewpoint of a Zoologist.Inithefeaturedhisbiologicalspeciesconcept,defining species as groups of organisms capable of freely interbreeding with each other and producing viable offspring in the wild. Mayr’spaperattheColdSpringHarborsymposiumwastherefore amustforcontemporarystudentsofhumanevolution.Hemade several very pointed remarks that are worth recalling over years later. Mayr recognized that without fully appreciating the correctcategorizationofhumans,wewouldbeunabletounder- stand our evolution: ‘The whole problem of the origin of man depends, to a considerable extent, on the proper definition and vii the improbable primate evaluation of taxonomic categories.’ He recognized that the arrival of the fully upright human marked a significant and unprecedented departure from anything that had come before and surmised that this arrival in what he called a different adap- tive zone exposed humans to new selection pressures. This departure from all primate models that had preceded it, was so markedthatitdeservedahighertaxonomiccategorythanthatof species. With Homo came a new genus and, I would argue, a highlyimprobableprimate.Mayrthenwentontomakearemark for which he has been criticized by palaeoanthropologists ever since. Mayr clearly stated that ‘Indeed, all the now available evidence can be interpreted as indicating that, in spite of much geographical variation, never more than one species of man existed on the earth at any one time’. Mayr, I will argue, was right even though today many scholars of our evolution would disagree,stillpreferringtoawardspeciesstatustofossilsofHomo based on morphological criteria. The possibleexceptionto Mayr’sstatementcould be theHob- bit on Flores. Its small stature may have prevented interbreeding withotherhumans,purelybecauseofphysicallimitations,butwe cannotbecertainofthis.Theapplicationofthebiologicalspecies concept to allopatric populations, those separated from each other by geographical or other barriers, has always been prob- lematic because it is impossible to know whether those popula- tions might be capable of interbreeding were these impediments removed. The Hobbit, isolated in a remote world almost taken out of a Jules Verne novel, is an example of an allopatric popu- lation whose taxonomic status is difficult to determine. Hobbit aside, what is clear now is that Homo sapiens was a polytypic species, that is, highly geographically variable but all individuals viii preface capable of reproducing with each other as Mayr recognized, but no different from many other similar examples from the natural world.Butthereisnoevidencetosuggestthatthesepopulations were ever distinct enough for interbreeding to have been pre- vented.Thebastionofthepalaeoanthropologistswhosupported the many species of Man, the Neanderthals, collapsed with the clear evidence that our own lineage interbred with theirs to a sufficientdegreethatthesignalwasretainedinourgenome.Then cametheDenisovans,anotherancientlineagenowalsoshownto have exchanged genes with our own. If these populations were abletointerbreed,andbehavelikeoneandthesamespecies,after hundreds of thousands of years of isolation, then the question is resolved and Mayr shown to have been right. Not everyone agrees. Some palaeoanthropologists maintain a multi-species view while accepting that there was interbreeding. They argue that hybridization can occur in the wild today between closely related species.2 Mayr understood well that dif- ferent species sometimes hybridize but they form stable hybrid zones which are confined geographically.3 However, this is not whatweobservewiththeNeanderthals,theDenisovans,andour ancestors. If the genetic signal has been retained right down to today, interbreeding would not have been an isolated affair. Some notable palaeoanthropologists have followed Mayr in declaringHomo sapiens to havebeena polytypicspeciesthrough- out its nearly -million-year-old history. Emiliano Aguirre, the great scientist who discovered the spectacular site of Atapuerca was one and Milford Wolpoff in Michigan was another.4 When Ifirstenteredthisworldofthestudyofourevolution,backinthe early s, the case seemed closed. The Neanderthals were con- sidered a different species from us and so were a number of ix
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